Magnetic core, inductor, and emi filter comprising same

ABSTRACT

An inductor according to an embodiment of the present invention comprises: a first magnetic body having a toroidal shape, and including a ferrite; and a second magnetic body disposed on an outer circumferential surface or an inner circumferential surface of the first magnetic body, wherein the second magnetic body includes: resin material and a plurality of layers of metal ribbons wound along the circumferential direction of the first magnetic body, wherein the resin material comprises a first resin material disposed to cover an outer surface of the plurality of layers of metal ribbons, and a second resin material disposed in at least a part of a plurality of layers of interlayer spaces.

TECHNICAL FIELD

The present disclosure relates to a magnetic core, an inductor, and anEMI filter including the same.

BACKGROUND ART

An inductor is one of electronic components that are used in printedcircuit boards, and may be applied to resonance circuits, filtercircuits, power circuits, etc. due to the electromagneticcharacteristics thereof.

Meanwhile, an electromagnetic interference (EMI) filter used in a powerboard serves to transmit a signal necessary for the operation of acircuit and to remove noise.

FIG. 1 is a block diagram showing a construction whereby a general powerboard equipped with an EMI filter is connected to a power source and toa load.

Noise transmitted from the power board of the EMI filter shown in FIG. 1may be largely classified into radiative noise of 30 MHz to 1 GHzradiated from the power board and conductive noise of 150 kHz to 30 MHzconducted via a power line.

A conductive noise transmission mode may be classified into adifferential mode and a common mode. Among these modes, common-modenoise travels and returns along a large loop. Thus, the common-modenoise may affect electronic devices that are located far away, even whenthe amount thereof is small. Such common-mode noise is generated byimpedance imbalance of a wiring system, and becomes remarkable at highfrequencies.

In order to remove common-mode noise, an inductor that is applied to theEMI filter shown in FIG. 1 generally uses a toroidal-shaped magneticcore that includes a Mn—Zn-based ferrite material. Since Mn—Zn-basedferrite has a high magnetic permeability within a range from 100 kHz to1 MHz, it is capable of effectively removing common-mode noise.

FIG. 2 is a perspective view of a general inductor 100.

Referring to FIG. 2, the inductor 100 may include a magnetic core 110and a coil 120 wound around the magnetic core 110.

The magnetic core 110 may have a toroidal shape, and the coil 120 mayinclude a first coil 122 wound around the magnetic core 110 and a secondcoil 124 wound so as to be opposite the first coil 122. Each of thefirst coil 122 and the second coil 124 may be wound around a top surfaceS1, a side surface S2 and a bottom surface S3 of the toroidal-shapedmagnetic core 110.

The magnetic core 110 may further include a bobbin (not shown) forinsulating the magnetic core 110 from the coil 120, and the coil 120 maybe configured as a conductive wire coated on the surface thereof with aninsulating material.

FIG. 3 is an exploded perspective view of the magnetic core shown inFIG. 2, in which a bobbin is further included, and FIG. 4 is aperspective view showing the process of forming the magnetic core shownin FIG. 3.

Referring to FIG. 3, the magnetic core 110 may be accommodated in thebobbin 130. The bobbin 130 may include an upper bobbin 132 and a lowerbobbin 134.

Next, referring to FIG. 4(a), in the state in which the upper bobbin132, the magnetic core 110 and the lower bobbin 132 are provided in theconfiguration shown in FIG. 3, the magnetic core 110 may be disposed onthe bottom surface of the lower bobbin 132. Subsequently, as shown inFIG. 4(b), the upper bobbin 131 may be coupled to the product shown inFIG. 4(a). In this case, the respective components may be adhered toeach other using an adhesive material.

Various efforts have been made to improve the performance of theinductor described above by, for example, forming the magnetic core 110using different materials. In one example, a Fe—Si-based metal ribbonmay be disposed on at least a portion of the surface of atoroidal-shaped magnetic core in which a Mn—Zn-based ferrite material isincluded, as described above. However, a metal ribbon is usuallysubjected to heat treatment at a high temperature (e.g. 500° C. to 600°C.) in order to obtain strong magnetic properties (i.e. high magneticpermeability). However, a metal ribbon that has undergonehigh-temperature heat treatment has improved magnetic properties but hasexcessively reduced strength, and is thus brittle and poorly resistantto small impacts, thereby making the conveyance and treatment thereofvery difficult during the manufacturing process, resulting indeterioration in workability and yield of finished products.

DISCLOSURE Technical Problem

An object of the present disclosure is to provide a magnetic core parthaving improved magnetic properties and strength, an inductor, and anEMI filter including the same.

Technical Solution

An inductor according to an embodiment includes a first magnetic bodyhaving a toroidal shape and including ferrite and a second magnetic bodydisposed on the outer circumferential surface or the innercircumferential surface of the first magnetic body. The second magneticbody includes a metal ribbon wound in multiple layers in thecircumferential direction of the first magnetic body and a resinmaterial. The resin material includes a first resin material disposed soas to cover the outer surface of the metal ribbon wound in the multiplelayers and a second resin material disposed in at least a part of aninterlayer space in the multiple layers.

For example, the first magnetic body may include Mn—Zn-based ferrite,the second magnetic body may include a Fe—Si-based metal ribbon, and thesecond resin material may be disposed in a region corresponding to 0% to5% of the overall height of the second magnetic body and a regioncorresponding to 95% to 100% of the overall height of the secondmagnetic body in a direction from the bottom surface toward the topsurface of the second magnetic body.

For example, the thickness of the first magnetic body in the diameterdirection may be greater than the thickness of the second magnetic bodyin the diameter direction, and the thickness of the second magnetic bodyin the diameter direction may be greater than the thickness of the firstresin material in the diameter direction.

For example, the thickness of the first resin material may be 20 μm to30 μm.

For example, the height of the first resin material may be greater thanthe height of the second magnetic body.

For example, the second resin material may be disposed in a regioncorresponding to 15% to 30% of the interlayer space in the multiplelayers.

For example, the second resin material may be disposed in a regioncorresponding to 20% to 25% of the interlayer space in the multiplelayers.

An EMI filter according to an embodiment may include an inductor and acapacitor. The inductor may include a first magnetic body having atoroidal shape and including ferrite and a second magnetic body disposedon the outer circumferential surface or the inner circumferentialsurface of the first magnetic body. The second magnetic body may includea metal ribbon wound in multiple layers in the circumferential directionof the first magnetic body and a resin material. The resin material mayinclude a first resin material disposed so as to cover the outer surfaceof the metal ribbon wound in the multiple layers and a second resinmaterial disposed in at least a part of an interlayer space in themultiple layers.

For example, the first magnetic body may include Mn—Zn-based ferrite,the second magnetic body may include a Fe—Si-based metal ribbon, and thesecond resin material may be disposed in a region corresponding to 0% to5% of the overall height of the second magnetic body and a regioncorresponding to 95% to 100% of the overall height of the secondmagnetic body in a direction from the bottom surface toward the topsurface of the second magnetic body.

For example, a portion of the second resin material may be disposed in aregion corresponding to 15% to 30% of the interlayer space in themultiple layers.

Advantageous Effects

In an inductor and an EMI filter including the same according to anembodiment, a magnetic core having the shape of a metal ribbon wound inmultiple layers is coated with a resin material, thus improving thestrength and magnetic properties thereof.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a construction whereby a general powerboard equipped with an EMI filter is connected to a power source and toa load.

FIG. 2 is a perspective view of a general inductor.

FIG. 3 is an exploded perspective view of the magnetic core shown inFIG. 2, in which a bobbin is further included.

FIGS. 4(a) and 4(b) are perspective views showing the process of formingthe magnetic core shown in FIG. 3.

FIG. 5 illustrates a perspective view and a cross-sectional view of amagnetic core according to an embodiment of the present disclosure.

FIG. 6 is a view showing the process of forming the magnetic core ofFIG. 5.

FIGS. 7, 8(a), 8(b), 8(c) and 9 are perspective views andcross-sectional views of magnetic cores according to other embodimentsof the present disclosure.

FIG. 10 is a graph showing the magnetic permeability and inductance of aferrite material and a metal ribbon material.

FIG. 11 shows cross-sectional images showing an area occupied by epoxyin an interlayer space depending on the dilution ratio of an epoxycoating solution according to an embodiment.

FIG. 12 is a view showing areas in which samples according to theembodiment were measured.

FIGS. 13(a) to 13(d) show the measurement results in the areas of FIG.12.

FIG. 14 is an example of an EMI filter including the inductor accordingto the embodiment.

BEST MODE

Exemplary embodiments can be variously changed and embodied in variousforms, in which illustrative embodiments are shown. However, exemplaryembodiments should not be construed as being limited to the embodimentsset forth herein, and any changes, equivalents or alternatives which arewithin the spirit and scope of the embodiments should be understood asfalling within the scope of the embodiments.

It will be understood that although the terms “second”, “first”, etc.may be used herein to describe various elements, these elements shouldnot be construed as being limited by these terms. These terms are onlyused to distinguish one element from another element. For example, asecond element may be termed a first element, and a first element may betermed a second element, without departing from the teachings of theembodiments. The term “and/or” includes any and all combinations of oneor more of the associated listed items.

It will be understood that when an element is referred to as being“connected to” or “coupled to” another element, it may be directlyconnected or coupled to the other element, or intervening elements maybe present. In contrast, when an element is referred to as being“directly connected to” or “directly coupled to” another element orlayer, there are no intervening elements present.

In the description of the embodiments, it will be understood that whenan element, such as a layer (film), a region, a pattern or a structure,is referred to as being “on” or “under” another element, such as asubstrate, a layer (film), a region, a pad or a pattern, the term “on”or “under” means that the element is “directly” on or under anotherelement, or is “indirectly” formed such that an intervening element mayalso be present. It will also be understood that criteria of on or underis on the basis of the drawing. The thickness or size of a layer (film),a region, a pattern, or a structure shown in the drawings may beexaggerated, omitted or schematically drawn for the convenience andclarity of explanation, and may not accurately reflect the actual size.

The terms used in the present specification are used for explainingspecific exemplary embodiments, not limiting the present inventiveconcept. Thus, the singular expressions in the present specificationinclude the plural expressions unless clearly specified otherwise incontext. In the specification, the terms “comprising” or “including”shall be understood to designate the presence of particular features,numbers, steps, operations, elements, parts, or combinations thereof butnot to preclude the presence or addition of one or more other features,numbers, steps, operations, elements, parts, or combinations thereof.

Unless otherwise defined, all terms including technical and scientificterms used herein have the same meanings as those commonly understood byone of ordinary skill in the art to which this inventive conceptpertains. It will be further understood that terms, such as thosedefined in commonly used dictionaries, should be interpreted as havingmeanings consistent with their meanings in the context of the relevantart, and are not to be interpreted in an idealized or overly formalsense unless expressly so defined herein.

Hereinafter, embodiments will be described in detail with reference tothe accompanying drawings. The same elements are denoted by the samereference numerals in the drawings, and a repeated explanation thereofwill not be given.

According to an embodiment of the present disclosure, a magnetic coremay include a first magnetic body and a second magnetic body formed ofdifferent materials from each other. Here, the second magnetic body maybe disposed on at least a portion of the surface of the first magneticbody, and may include a metal ribbon wound in multiple layers. Thesecond magnetic body according to the embodiment may include a resinmaterial in order to solve the problem of reduced strength of the metalribbon, wound in multiple layers, after heat treatment. The resinmaterial may include a resin material covering the outer surface of themetal ribbon wound in multiple layers and a resin material disposed inat least a part of an interlayer space in the multiple layers. Here, aninterlayer space may be a space between two ribbon layers that areadjacent to each other in the centrifugal direction when the metalribbon is wound, specifically a space formed between the outercircumferential surface of a layer relatively close to the circle centerand the inner circumferential surface of a layer relatively far from thecircle center. A method of forming the resin material and the propertiesof the resin material will be described later in more detail. First,various embodiments in which mutually different magnetic bodiesaccording to the embodiments of the present disclosure constitute themagnetic core will be described with reference to FIGS. 5 to 8. Forconvenience of description, an illustration of the resin material isomitted from FIGS. 5 to 7.

FIG. 5 illustrates a perspective view and a cross-sectional view of amagnetic core according to an embodiment of the present disclosure, FIG.6 is a view showing the process of forming the magnetic core of FIG. 5,and FIGS. 7 to 9 are perspective views and cross-sectional views ofmagnetic cores according to other embodiments of the present disclosure.

Referring to FIG. 5, a magnetic core 800 may include a first magneticbody 810 and a second magnetic body 820. The first magnetic body 810 andthe second magnetic body 820 may be formed of different materials, andthe second magnetic body 820 may be disposed on at least a portion ofthe surface of the first magnetic body 810. In this case, the secondmagnetic body 820 may have a higher saturation magnetic flux densitythan the first magnetic body 810.

Here, the first magnetic body 810 may include ferrite, and the secondmagnetic body 820 may include a metal ribbon. Here, the magneticpermeability (μ) of ferrite may be 2,000 to 15,000, and the magneticpermeability (μ) of the metal ribbon may be 100,000 to 150,000. Forexample, the ferrite may be Mn—Zn-based ferrite, and the metal ribbonmay be a Fe-based nanocrystalline metal ribbon. The Fe-basednanocrystalline metal ribbon may be a nanocrystalline metal ribbonincluding Fe and Si. The thickness of the metal ribbon may be 15 μm to20 μm, without being limited thereto.

In this case, each of the first magnetic body 810 and the secondmagnetic body 820 has a toroidal shape, and the second magnetic body 820may include a second outer magnetic body 822 disposed on the outercircumferential surface S2 of the first magnetic body 810 and a secondinner magnetic body 824 disposed on the inner circumferential surface S4of the first magnetic body 810.

In this case, each of the thicknesses of the second outer magnetic body822 and the second inner magnetic body 824 is smaller than the thicknessof the first magnetic body 810. The magnetic permeability of themagnetic core 800 may be adjusted by adjusting at least one of the ratioof the thickness of the second outer magnetic body 822 to the thicknessof the first magnetic body 810 or the ratio of the thickness of thesecond inner magnetic body 824 to the thickness of the first magneticbody 810.

In order to manufacture such a magnetic core, as shown in FIG. 6, twosecond magnetic bodies 822 and 824 are separately prepared. Each of thesecond magnetic bodies 822 and 824 may be configured as a metal ribbonwound in multiple layers and coated with a resin material. Among theprepared second magnetic bodies 822 and 824, the second inner magneticbody 824 corresponding to the inner circumferential surface S4 of thefirst magnetic body 810 having a toroidal shape may be inserted into ahollow portion in the first magnetic body 810, and the first magneticbody 810 may be inserted into a hollow portion in the second outermagnetic body 822 corresponding to the outer circumferential surface S2of the first magnetic body 810. Of course, the order in which the secondmagnetic bodies are coupled to the first magnetic body 810 may bechanged.

In this case, the outer circumferential surface S2 of the first magneticbody 810 may be adhered to the second outer magnetic body 822, and theinner circumferential surface S4 of the first magnetic body 810 may beadhered to the second inner magnetic body 824 using an adhesive. In thiscase, the adhesive may be an adhesive including at least one ofepoxy-based resin, acrylic-based resin, silicon-based resin, or varnish.As such, when the mutually different magnetic bodies are adhered to eachother using an adhesive, it is possible to prevent the performance frombeing deteriorated by physical vibration.

Here, as shown in FIG. 5, each of the second magnetic bodies 822 and 824may include a metal ribbon wound multiple turns so as to be stacked inmultiple layers. The thickness and magnetic permeability of the secondmagnetic bodies 822 and 824 may vary depending on the number of layersin which the metal ribbon is stacked, and accordingly, the magneticpermeability of the magnetic core 800 may vary, and the noise removalperformance of an EMI filter equipped with the magnetic core 800 mayvary.

That is, when the thicknesses of the second magnetic bodies 822 and 824are increased, the noise removal performance may be improved. Using thisprinciple, the number of layers in which the metal ribbon is stacked maybe adjusted such that the thicknesses of the second magnetic bodies 822and 824 disposed in a region in which the coil is wound are greater thanthe thicknesses of the second magnetic bodies 822 and 824 disposed in aregion in which the coil is not wound.

The number of layers in which the metal ribbon is stacked may beadjusted by changing the number of windings, the starting point ofwinding, and the ending point of winding. The relationship between thestarting point of winding and the ending point of winding will bedescribed based on the second outer magnetic body 822, disposed on theouter circumferential surface S2 of the first magnetic body 810, asshown in FIG. 5(a). Of course, as described above, winding of the secondouter magnetic body 822 and formation of the resin material (not shown)thereon are completed before the second outer magnetic body 822 iscoupled to the first magnetic body 810. However, for convenience ofdescription, it is assumed that winding starts from a certain point onthe outer circumferential surface of the first magnetic body 810.

When the second outer magnetic body 822, which is a metal ribbon, iswound one turn from the starting point of winding, the second outermagnetic body 822 may include a one-layered metal ribbon. When thesecond outer magnetic body 822 is wound two turns from the startingpoint of winding, the second outer magnetic body 822 may include atwo-layered metal ribbon. Meanwhile, when the starting point of windingand the ending point of winding do not coincide with each other, forexample, when the second outer magnetic body 822 is wound one and a halfturns from the starting point of winding, the second outer magnetic body822 includes a region in which the metal ribbon is stacked in a singlelayer and a region in which the metal ribbon is stacked in two layers.Alternatively, when the second outer magnetic body 822 is wound two anda half turns from the starting point of winding, the second outermagnetic body 822 includes a region in which the metal ribbon is stackedin two layers and a region in which the metal ribbon is stacked in threelayers. In this case, if the coil is disposed on the region in which thenumber of layers in which the metal ribbon is stacked is greater, thenoise removal performance of an EMI filter to which the magnetic core800 according to the embodiment of the present disclosure is applied maybe further improved.

For example, in the case in which the magnetic core 800 has a toroidalshape and the first coil 122 and the second coil 124 are wound so as tobe symmetrical to each other around the magnetic core 800, the firstcoil 122 may be disposed on a region in which the number of stackedlayers of the second outer magnetic body 822, which is disposed on theouter circumferential surface of the first magnetic body 810, isrelatively large, and the second coil 124 may be disposed on a region inwhich the number of stacked layers of the second inner magnetic body824, which is disposed on the inner circumferential surface of the firstmagnetic body 810, is relatively large. Accordingly, each of the firstcoil 122 and the second coil 124 may be disposed on a region in whichthe number of stacked layers of a respective one of the second magneticbodies 822 and 824 is relatively large, but may not be disposed on aregion in which the number of stacked layers of a respective one of thesecond magnetic bodies 822 and 824 is relatively small, therebyachieving improved noise removal performance.

Although the second outer magnetic body 822 and the second innermagnetic body 824 are illustrated as being made of the same material andhaving the same thickness, the disclosure is not limited thereto. Thesecond outer magnetic body 822 and the second inner magnetic body 824may have different materials or different values of magneticpermeability, and may have different thicknesses. Therefore, themagnetic permeability of the magnetic core 800 may have a wide range ofvalues.

Meanwhile, as shown in FIG. 7, the height h1 of the first magnetic body810 may be greater than the height h2 of the second magnetic body 820.To this end, in the process of manufacturing the second magnetic body820, a metal ribbon having a width less than the height h1 of the firstmagnetic body 810 may be wound. Accordingly, the second outer magneticbody 822 may not be disposed on the boundary between the top surface S1and the outer circumferential surface S2 of the first magnetic body 810and the boundary between the bottom surface S3 and the outercircumferential surface S2 of the first magnetic body 810, and thesecond inner magnetic body 824 may not be disposed on the boundarybetween the top surface S1 and the inner circumferential surface S4 ofthe first magnetic body 810 and the boundary between the bottom surfaceS3 and the inner circumferential surface S4 of the first magnetic body810. Therefore, the second outer magnetic body 822 may be prevented fromcracking along the boundary between the top surface S1 and the outercircumferential surface S2 of the first magnetic body 810, the boundarybetween the bottom surface S3 and the outer circumferential surface S2of the first magnetic body 810, the boundary between the top surface S1and the inner circumferential surface S4 of the first magnetic body 810,or the boundary between the bottom surface S3 and the innercircumferential surface S4 of the first magnetic body 810.

Alternatively, as shown in FIG. 8, the second magnetic body 820 may bedisposed only on the outer circumferential surface S2 of the firstmagnetic body 810. Alternatively, as shown in FIG. 9, the secondmagnetic body 820 may be disposed only on the inner circumferentialsurface S4 of the first magnetic body 810.

With the above-described configuration, in which the magnetic core 800includes the mutually different magnetic bodies having different valuesof magnetic permeability, it is possible to remove noise over a widefrequency band. In particular, compared to a toroidal-shaped magneticcore that is formed only of Mn—Zn-based ferrite, the magnetic coreaccording to the embodiment is capable of effectively removinghigh-frequency noise by preventing concentration of magnetic flux on thesurface thereof, and is capable of being applied to high-power productsdue to the low degree of internal saturation. Further, the performanceof the magnetic core 800 may be adjusted by adjusting the values ofmagnetic permeability or the volume ratios of the first magnetic body810 and the second magnetic body 820.

Meanwhile, referring to FIG. 10, it can be seen that a magnetic coreincluding a ferrite material and a metal ribbon material, which havedifferent values of magnetic permeability according to frequency, hashigh inductance in a predetermined frequency range, and thus improvesnoise removal performance.

The arrangement relationship between the first magnetic body and thesecond magnetic body according to the embodiments has been describedabove. Hereinafter, a resin material of the second magnetic bodyaccording to an embodiment of the present disclosure will be describedin more detail.

According to an embodiment, the resin material may be formed byperforming heat treatment on a metal ribbon wound in multiple layers,dipping the product that has undergone heat treatment in a coatingsolution, and drying the same. Depending on the embodiment, the dryingprocess may include performing a thermal drying process at a temperatureof 60° C. to 150° C.

As shown in FIG. 8(c), in the second magnetic body 820, the resinmaterial R may be disposed on the outer surface (the top surface, thebottom surface, the inner circumferential surface, and the outercircumferential surface) of the wound metal ribbon MR, and may also bedisposed between the wound layers (not shown) of the metal ribbon.

According to an embodiment, the coating solution may be a mixed solutionin which an epoxy resin and a diluent are mixed at a predeterminedratio. The diluent is not limited to any specific component, so long asit is capable of dissolving the epoxy resin. Tables 1 to 4 below showexamples of the result of measuring an inductance reduction rate byvarying the ratio of the epoxy resin to the diluent.

TABLE 1 Ratio of Epoxy to Inductance (@16 kHz) Reduction Diluent SampleBefore Dipping After Dipping Rate (%) 5:5 #1 65.52 45.16 −31.08 #2 60.4342.78 −29.2 #3 59.42 41.72 −29.79 #4 65.25 46.03 −29.46 #5 64.23 47.08−26.7 #6 55.08 41.16 −25.28 #7 62.06 41.94 −32.42 #8 64.57 43.49 −32.64#9 63.11 43.49 −31.09 #10  72.68 50.88 −29.99 Avg. 63.23 44.37 −29.76

TABLE 2 Ratio of Epoxy to Inductance (@16 kHz) Reduction Diluent SampleBefore Dipping After Dipping Rate (%) 3:7 #1 60.96 58.96 −3.28 #2 76.3666.32 −13.15 #3 75.26 64.16 −14.75 #4 64.41 49.25 −23.54 #5 58.02 50.02−13.79 #6 61.46 45.99 −25.18 #7 51.35 44.05 −14.22 #8 52.56 45.64 −13.15#9 53.93 46.08 −14.56 #10  49.89 42.64 −14.54 Avg. 60.42 51.31 −15.02

TABLE 3 Ratio of Epoxy to Inductance (@16 kHz) Reduction Diluent SampleBefore Dipping After Dipping Rate (%) 2:8 #1 60.92 53.93 −11.47 #2 55.453.68 −3.1 #3 49.27 44.4 −9.88 #4 45.79 48.19 5.24 #5 58.26 54.78 −5.97#6 61.64 54.8 −11.1 #7 62.14 56.59 −8.93 #8 53.22 51.44 −3.34 #9 49.3546.89 −4.98 #10  44.92 43.28 −3.65 Avg. 54.09 50.8 −5.72

TABLE 4 Ratio of Epoxy to Inductance (@16 kHz) Reduction Diluent SampleBefore Dipping After Dipping Rate (%) 1:9 #1 49.14 46.18 −6.02 #2 44.4742.21 −5.09 #3 38.33 36.68 −4.3 #4 38.92 36.43 −6.39 #5 40.07 36.93−7.85 #6 49.13 49.68 1.13 #7 57.5 55.41 −3.63 #8 44.08 42.13 −4.43 #941.62 41.4 −0.54 #10  44.62 40.23 −9.84 Avg. 44.79 42.73 −4.7

Referring to Tables 1 to 4, it can be seen that the higher the contentof the epoxy resin, the higher the inductance reduction rate and thatthe higher the content of the diluent, the lower the inductancereduction rate. Specifically, when the ratio of the epoxy resin to thediluent was 5:5, the inductance reduction rate was approximately 30percent, and when the ratio of the epoxy resin to the diluent was 3:7,the inductance reduction rate was approximately 15 percent. However,when the ratio of the epoxy resin to the diluent was 2:8 and when theratio of the epoxy resin to the diluent was 1:9, slightly differentinductance reduction rates, which were 5.72% and 4.7%, respectively,were obtained. That is, relatively low inductance reduction rates wereobtained.

Next, the strength of each diluent is shown in Table 5.

TABLE 5 Ratio of Epoxy to Diluent Sample Before Dipping 5:5 3:7 2:8 1:9#1 75 757 515 386 240 #2 56 806 494 511 297 #3 62 770 544 420 250 #4 68774 580 583 213 #5 80 857 482 467 222 #6 61 821 543 520 236 #7 88 890490 478 221 #8 69 874 340 478 234 #9 76 745 422 460 219 #10  63 717 499425 174 Avg. 69.8 801.1 490.9 472.8 230.6

Table 5 shows the external force in units of “g”, by which a metalribbon, which has been wound 15 turns and has undergone heat treatment,is damaged when a specific point on the outer circumferential surface ofthe metal ribbon is pressed. Referring to Table 5, it can be seen that ametal ribbon before being dipped in a coating solution was damaged whenexternal force of about 70 g was applied thereto, but that the strengththereof was increased about 3 times to 10 times or more depending on theratio of the epoxy resin to the diluent.

The reason for the difference in the increase in strength depending onthe dilution ratio is that, when a metal ribbon is pulled up afterdipping, a larger amount of epoxy remains on the edges of the metalribbon due to the difference in viscosity of the epoxy resin dependingon the dilution ratio of a coating solution (i.e. a dipping solution).Another reason is an increase in the amount of epoxy resin that entersthe interlayer space between multiple layers of the wound metal ribbonin the dipping solution. Furthermore, the volume of the epoxy resinincreases in the interlayer space between the multiple layers of thewound metal ribbon during a drying process, which increases finecracking in the metal ribbon, resulting in reduced inductance. This willbe described with reference to FIGS. 11 to 13. Although not shown, whenthe overall height of the second magnetic body 820 is defined as thedistance from the bottom surface to the top surface of the secondmagnetic body 820, the resin material, which is disposed in theinterlayer space in the wound ribbon in FIGS. 11 to 13, may be disposedin a region corresponding to 0% to 5% of the overall height of thesecond magnetic body 820 and a region corresponding to 95% to 100% ofthe overall height of the second magnetic body 820 in a direction fromthe bottom surface toward the top surface of the second magnetic body820. Preferably, the resin material may be disposed in a regioncorresponding to 0% to 15% of the overall height of the second magneticbody 820 and a region corresponding to 85% to 100% of the overall heightof the second magnetic body 820 in a direction from the bottom surfacetoward the top surface of the second magnetic body 820. More preferably,the resin material may be disposed in a region corresponding to 0% to30% of the overall height of the second magnetic body 820 and a regioncorresponding to 70% to 100% of the overall height of the secondmagnetic body 820 in a direction from the bottom surface toward the topsurface of the second magnetic body 820. When the resin material isdisposed in a region corresponding to 31% to 69% of the overall heightof the second magnetic body 820 in a direction from the bottom surfacetoward the top surface of the second magnetic body 820, the improvementof strength and the inductance reduction rate may be insufficient.

FIG. 11 shows cross-sectional images showing the area occupied by epoxyin an interlayer space depending on the dilution ratio of an epoxycoating solution according to the embodiment. FIG. 11 shows enlargedimages of the cross-section of the second magnetic body when the secondmagnetic body is cut in a circumferential direction after a metal ribbonwound 15 turns is dipped in epoxy coating solutions having differentrespective dilution ratios. Further, in FIG. 11, the lower end of eachof the images is oriented toward the center of a circle, the upper imagecorresponding to each dilution ratio is an image showing the overallshape of a 15-layered metal ribbon, the lower image corresponding toeach dilution ratio is a further enlarged image showing only a 5-layeredmetal ribbon, and circles in each lower image indicate regions in whichepoxy resin is disposed.

Referring to FIG. 11, when the ratio of the epoxy to the diluent is 1:9,epoxy resin is disposed in a region corresponding to about 10% of theentirety of the space between the ribbon layers that are adjacent toeach other in the centrifugal direction, i.e. the interlayer space. Whenthe ratio of the epoxy to the diluent is 2:8, epoxy resin is disposed ina region corresponding to about 25% of the entirety of the interlayerspace. When the ratio of the epoxy to the diluent is 3:7, epoxy resin isdisposed in a region corresponding to about 30% of the entirety of theinterlayer space. When the ratio of the epoxy to the diluent is 5:5,epoxy resin is disposed in a region corresponding to about 50% of theentirety of the interlayer space.

Referring to FIG. 11, it can be seen that the strength varies dependingon the area occupied by the epoxy resin in the interlayer space.

Hereinafter, the inductance reduction rates shown in Tables 1 to 4 andthe increases in strength shown in Table 5 will be compared in detail.

When the ratio of the epoxy to the diluent was 5:5, the strength was thehighest, but the inductance reduction rate was too high. When the ratioof the epoxy to the diluent was 1:9, the inductance reduction rate wasthe lowest, but the degree of increase in strength was low.

Further, when the ratios of the epoxy to the diluent were 2:8 and 1:9,they exhibited improved effects in terms of the inductance reductionrate, and when the ratios of the epoxy to the diluent were 2:8 and 3:7,they exhibited improved effects in terms of the increase in strength.

In conclusion, when the ratio of the epoxy to the diluent was 2:8, itexhibited an improved inductance reduction rate, which was similar tothat when the ratio was 1:9, and exhibited increased strength, which wassimilar to that when the ratio was 3:7. Thus, it can be seen that themost desirable ratio of the epoxy to the diluent is 2:8.

Hereinafter, the area occupied by the epoxy in the interlayer space whenthe ratio of the epoxy to the diluent is 2:8 will be described in moredetail with reference to FIGS. 12 and 13.

FIG. 12 is a view showing areas in which samples according to theembodiment were measured, and FIG. 13 shows the measurement results inthe areas of FIG. 12.

FIG. 12 is a plan view of the second magnetic body 820 dried after beingdipped in a coating solution having a dilution ratio of 2:8 according tothe embodiment. In order to measure the area occupied by epoxy in theinterlayer space, one second magnetic body 820 was divided into fourareas Area_1 to Area_4, and the cross-section of each area taken in acircumferential direction was photographed. Therefore, the area occupiedby epoxy in the interlayer space was measured 4 times using one sampleof the second magnetic body, and a total of 20 measurement processeswere performed using 5 samples.

FIG. 13 shows the images of some samples captured during the measurementprocesses. FIG. 13 shows enlarged images of the cross-section of thesecond magnetic body when the second magnetic body is cut in acircumferential direction after a metal ribbon wound 15 turns is dippedin an epoxy coating solution having a dilution ratio of 2:8. Further, inFIG. 13, the lower end of each of the images is oriented toward thecenter of a circle, each upper image shows the cross-section, a portionof which is shown through a lower image in detail, each lower image is afurther enlarged image showing only a 5-layered metal ribbon, andcircles in each lower image indicate regions in which epoxy resin isdisposed.

Referring to FIG. 13(a), the epoxy resin occupies an area correspondingto 15% of the interlayer space. Referring to FIG. 13(b), the epoxy resinoccupies an area corresponding to 20% of the interlayer space. Referringto FIG. 13(c), the epoxy resin occupies an area corresponding to 25% ofthe interlayer space. Referring to FIG. 13(d), the epoxy resin occupiesan area corresponding to 30% of the interlayer space.

In conclusion, when the dilution ratio is 2:8, the area occupied by theepoxy in the interlayer space corresponds to 15% to 30% of theinterlayer space, which is a range including the maximum value and theminimum value. The results of 20 measurement processes are shown inTable 6 below.

TABLE 6 Sample Area_1 Area_2 Area_3 Area_4 Total #1 15 25 30 25 #2 25 2025 20 #3 25 15 25 20 #4 30 30 25 30 #5 25 25 20 25 Avg. 24 23 25 24 24

Referring to Table 6, among a total of 20 experiments, 15% was measuredin two experiments, 20% was measured in four experiments, 25% wasmeasured in seven experiments, and 30% was measured in threeexperiments. Therefore, when the dilution ratio is 2:8, the areaoccupied by the epoxy in the interlayer space may correspond to 15% to30% of the interlayer space, preferably 20% to 25%, and more preferably23% to 25%. Further, although not shown, the thickness of an outercoating layer of the second magnetic body may be 10 μm to 40 μm, andpreferably 20 μm to 30 μm. When the thickness is less than 10 μm, thestrength may decrease, thus leading to damage to the metal ribbon. Whenthe thickness is greater than 40 μm, the inductance reduction rate mayincrease, thus leading to deterioration in performance.

Meanwhile, the inductor according to the above-described embodiment maybe included in a line filter. For example, the line filter may be a linefilter for reducing noise, which is applied to an AC-to-DC converter.FIG. 14 is an example of an EMI filter including the inductor accordingto the embodiment.

Referring to FIG. 14, an EMI filter 2000 may include a plurality ofX-capacitors Cx, a plurality of Y-capacitors Cy, and an inductor L.

The X-capacitors Cx are respectively disposed between a first terminalP1 of a live line LIVE and a third terminal P3 of a neutral line NEUTRALand between a second terminal P2 of the live line LIVE and a fourthterminal P4 of the neutral line NEUTRAL.

The plurality of Y-capacitors Cy may be disposed in series between thesecond terminal P2 of the live line LIVE and the fourth terminal P4 ofthe neutral line NEUTRAL.

The inductor L may be disposed between the first terminal P1 and thesecond terminal P2 of the live line LIVE and between the third terminalP3 and the fourth terminal P4 of the neutral line NEUTRAL. Here, theinductor L may be the inductor 100 according to the above-describedembodiment.

When common-mode noise is introduced thereinto, the EMI filter 2000removes the common-mode noise due to the combined impedancecharacteristics of the primary inductance and the Y-capacitor Cy. Here,the primary inductance of the live line LIVE may be obtained bymeasuring the inductance between the first and second terminals P1 andP2 in the state in which the third and fourth terminals P3 and P4 areopen, and the primary inductance of the neutral line NEUTRAL may beobtained by measuring the inductance between the third and fourthterminals P3 and P4 in the state in which the first and second terminalsP1 and P2 are open.

When differential-mode noise is introduced thereinto, the EMI filter2000 removes the differential-mode noise due to the combined impedancecharacteristics of the leakage inductance and the X-capacitor Cx. Here,the leakage inductance of the live line LIVE may be obtained bymeasuring the inductance between the first and second terminals P1 andP2 in the state in which the third and fourth terminals P3 and P4 areshort-circuited, and the leakage inductance of the neutral line NEUTRALmay be obtained by measuring the inductance between the third and fourthterminals P3 and P4 in the state in which the first and second terminalsP1 and P2 are short-circuited.

The inductor of the EMI filter 2000 according to the embodimentcorresponds to the inductor according to the above-describedembodiments.

The contents of the above-described embodiments may be applied to otherembodiments as long as they are not incompatible with one another.

While the present disclosure has been particularly shown and describedwith reference to exemplary embodiments thereof, these embodiments areonly proposed for illustrative purposes and do not restrict the presentdisclosure, and it will be apparent to those skilled in the art thatvarious changes in form and details may be made without departing fromthe essential characteristics of the embodiments set forth herein. Forexample, respective configurations set forth in the embodiments may bemodified and applied. Further, differences in such modifications andapplications should be construed as falling within the scope of thepresent disclosure as defined by the appended claims.

1. An inductor comprising: a first magnetic body having a toroidal shape, the first magnetic body comprising ferrite; and a second magnetic body disposed on an outer circumferential surface or an inner circumferential surface of the first magnetic body, wherein the second magnetic body comprises a metal ribbon wound in multiple layers in a circumferential direction of the first magnetic body and a resin material, and wherein the resin material comprises: a first resin material disposed so as to cover an outer surface of the metal ribbon wound in the multiple layers; and a second resin material disposed in at least a part of an interlayer space in the multiple layers.
 2. The inductor according to claim 1, wherein the first magnetic body comprises Mn—Zn-based ferrite, wherein the second magnetic body comprises a Fe—Si-based metal ribbon, and wherein the second resin material is disposed in a region corresponding to 0% to 5% of an overall height of the second magnetic body and a region corresponding to 95% to 100% of the overall height of the second magnetic body in a direction from a bottom surface toward a top surface of the second magnetic body.
 3. The inductor according to claim 1, wherein a thickness of the first magnetic body in a diameter direction is greater than a thickness of the second magnetic body in a diameter direction, and wherein the thickness of the second magnetic body in the diameter direction is greater than a thickness of the first resin material in a diameter direction.
 4. The inductor according to claim 3, wherein the thickness of the first resin material is 20 μm to 30 μm.
 5. The inductor according to claim 3, wherein a height of the first resin material is greater than a height of the second magnetic body.
 6. The inductor according to claim 1, wherein the second resin material is disposed in a region corresponding to 15% to 30% of the interlayer space in the multiple layers.
 7. The inductor according to claim 6, wherein the second resin material is disposed in a region corresponding to 20% to 25% of the interlayer space in the multiple layers. 8-10. (canceled)
 11. The inductor according to claim 1, further comprising: an adhesive disposed between the first magnetic body and the second magnetic body.
 12. The inductor according to claim 1, further comprising: a coil wound around the first magnetic body and the second magnetic body.
 13. The inductor according to claim 12, wherein the second magnetic body comprises a first region in which the coil is wound and a second region in which the coil is not wound.
 14. The inductor according to claim 13, wherein a number of layers of the metal ribbon in the first region is different from a number of layers of the metal ribbon in the second region.
 15. The inductor according to claim 14, wherein the number of layers of the metal ribbon in the first region is greater than the number of layers of the metal ribbon in the second region.
 16. An EMI filter comprising: an inductor; and a capacitor, wherein the inductor comprises: a first magnetic body having a toroidal shape, the first magnetic body comprising ferrite; and a second magnetic body disposed on an outer circumferential surface or an inner circumferential surface of the first magnetic body, wherein the second magnetic body comprises a metal ribbon wound in multiple layers in a circumferential direction of the first magnetic body and a resin material, and wherein the resin material comprises: a first resin material disposed so as to cover an outer surface of the metal ribbon wound in the multiple layers; and a second resin material disposed in at least a part of an interlayer space in the multiple layers.
 17. The EMI filter according to claim 16, wherein the first magnetic body comprises Mn—Zn-based ferrite, wherein the second magnetic body comprises a Fe—Si-based metal ribbon, and wherein the second resin material is disposed in a region corresponding to 0% to 5% of an overall height of the second magnetic body and a region corresponding to 95% to 100% of the overall height of the second magnetic body in a direction from a bottom surface toward a top surface of the second magnetic body.
 18. The EMI filter according to claim 17, wherein a portion of the second resin material is disposed in a region corresponding to 15% to 30% of the interlayer space in the multiple layers.
 19. The EMI filter according to claim 18, wherein the second resin material is disposed in a region corresponding to 20% to 25% of the interlayer space in the multiple layers.
 20. The EMI filter according to claim 16, further comprising: an adhesive disposed between the first magnetic body and the second magnetic body.
 21. The EMI filter according to claim 16, wherein the second magnetic body comprises a first region in which a coil is wound and a second region in which the coil is not wound.
 22. The EMI filter according to claim 21, wherein a number of layers of the metal ribbon in the first region is different from a number of layers of the metal ribbon in the second region.
 23. The EMI filter according to claim 22, wherein the number of layers of the metal ribbon in the first region is greater than the number of layers of the metal ribbon in the second region. 